Switching from 12V to 24V

[transmitterdan]

[QUOTE=coopec43;2767071]

Originally Posted by transmitterdan

Clive,

For avoidance of doubt, if you run 12V bilge pumps on 24V there is a serious serious risk of fire. Motors inside bilge pumps are designed for a given maximum voltage. Exceeding that voltage will destroy the motor in a relatively short time".


Thanks for that. I wouldn't mess around with voltages on bilge pumps where maybe a life depended on it.

Although others do it I'd be reluctant to use 24V on a 12V diaphragm (say) galley pump. (I wouldn't worry about the motor but I'd be worried the diaphragm wouldn't be able to handle the higher RPM).

As a matter of interest I checked the weight of a Rule 3700 GPH bilge pump - the 12V, 24V and 32V models. I would have expected the 12V model to be heavier than the other two (having heavier winding) but they are all the same weight at 5.4lb. Maybe a production line expediency.............?


Clive

Clive,

The bottom line is that you cannot double the voltage to 24 unless you replace every non-dual voltage rated component. 12V only devices are a fire hazard when operated at twice their rating. Anything you read on the Internet that contradicts that is "fake news".

[coopec43]

Well this is interesting. Apparently the rotational speed of a lot of DC motors is controlled by varying the voltage


What determines the speed of a DC motor?
Generally, the rotational speed of a DC motor is proportional to the EMF in its coil (= the voltage applied to it minus voltage lost on its resistance), and the torque is proportional to the current. Speed control can be achieved by variable battery tappings, variable supply voltage, resistors or electronic controls.


I intend putting 24V into my 12V starter, exhaust fans, (maybe a pump) and oscillating fans anyway so this is of academic interest only.


I imagine varying the voltage to a motor to change the RPM would be uneconomical battery energy wise but why doesn't it damage the DC motor?



Clive

[transmitterdan]

Clive,

All motors have a maximum input voltage and current. What you are reading should go like this:

The speed of a DC motor can be decreased by operating with voltage less than the maximum rated voltage.

But it does not follow that you can safely increase voltage as much as you like without consequence.

What you are planning will lead to very bad things happening. A 12V starter motor simply cannot handle 24V for long. Maybe if your engine starts on the first turn then the starter will not burn up. But the first time you have to crank the engine a while to get it started the starter will overheat and may catch fire. Why one would ever want to do that defies comprehension.

Exhaust fans and pump motors rated for 12V will definitely burn up running at 24V. Some oscillating fans are dual voltage rated because they have an internal voltage regulator. But most pumps and exhaust blowers are not so designed.

Your logic is so ridiculous that I seriously wonder if you are just having a go with me so this is my final post in this thread. For others reading this thread what Clive claims to believe, based on misreading stuff on the Internet, is wrong. Don't do what he is suggesting as it may very well result in fire and death. Really....